Currently the most common spray description is based on the Lagrangian discrete droplet method (DDM) (e.g., Rüger, et al., 2000). While the continuous phase is described by the standard Eulerian conservation equations, the transport of the dispersed phase is calculated by tracking the trajectories of a certain number of representative parcels (particles). A parcel consists of a number of droplets and it is assumed that all the droplets within one parcel have the same physical properties and behave equally when they move, breakup, or evaporate. The coupling between the liquid and the gaseous phases is achieved by source term exchange for mass, momentum, energy, and turbulence. Various submodels account for the effects of turbulent dispersion, coalescence, evaporation, and droplet breakup. The Lagrangian method is especially suitable for dilute sprays, but has shortcomings with respect to modeling of dense sprays. Further problems are reported connected with bad statistical convergence and also with dependence of the spray on grid size (Schmidt and Rutland, 2000).

Currently the most common spray description is based on the Lagrangian discrete droplet method [8]. While the continuous gaseous phase is described by the standard Eulerian conservation equations, the transport of the dispersed phase is calculated by tracking the trajectories of a certain number of representative parcels (particles). A parcel consists of a number of droplets and it is assumed that all the droplets within one parcel have the same physical properties and behave equally when they move, break up, hit a wall or evaporate. The coupling between the liquid and the gaseous phases is achieved by source term exchange for mass, momentum, energy and turbulence. Various sub-models account for the effects of turbulent dispersion [9], coalescence [10], evaporation [11], wall interaction [12] and droplet break up [13].

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This method is
especially suitable for dilute sprays, but has shortcomings
with respect to modeling of dense sprays where particle
interactions are strongly influenced by collisions and
parcels have to be rearranged and redistributed very often.
Further problems are reported connected with bad statistical
convergence [18] and also with dependence of the
propagation of the spray on grid size [19].